This invention relates to antennas and more especially it relates to mobile phone antennas.
Radio signal transmission from known integral mobile phone antennas may produce electromagnetic radiation in and around the head of a user at quite high levels. Radiation at especially high levels tends to be produced when the position of the head is such that it is interposed between the antenna and a base station to which the mobile phone is transmitting, whereby the signal received at the base station is effectively attenuated, so that a compensatory increase in transmitted signal power from the mobile phone is produced. The effect of this high concentration of radiation in and around the brain, although not fully understood, is generally accepted to be undesirable at the frequencies used, and consequently it is desirable that it should be avoided if at all possible.
It is an important object of the present invention to provide a mobile phone antenna wherein the aforesaid disadvantage of radiation concentration in or around a user""s head is obviated or at least very significantly reduced.
According to the present invention a mobile phone antenna comprises a belt which is adapted to be worn by a user and which comprises an antenna arrangement which in use is coupled to the mobile phone transceiver.
By positioning the antenna away from a user""s head and on a belt which may be worn around the waist of a user, radiation in the region of a user""s head is substantially reduced.
According to a preferred embodiment of the invention, the antenna arrangement comprises a plurality of antenna elements which are arranged in spaced apart relationship on a belt in a region inset from each end of the belt so as to provide for belt fixing, the elements being selectively fed via a signal feed network thereby to produce a predetermined beam pattern which tends to minimise the radiated signal power required thereby to optimise operational efficiency.
The signal feed network may comprise switches, which in use are arranged to be automatically operated so as to connect the mobile phone transmitter to an antenna element(s) which requires the least signal power for optimal operational efficiency.
Alternatively the signal feed network may comprise an adaptive weighting arrangement which serves selectively to weight the antenna elements so they tend to form an antenna beam in a direction which requires least radiated signal power.
The belt may comprise a strip of dielectric substrate material having on one side a conductive ground plane and on the other side the antenna arrangement and at opposing ends thereof a buckle and complementary piercing respectively, which are arranged mutually to co-operate for holding the belt in place around the body of a user.
The ground plane and or the antenna arrangement may be printed on opposite sides of the belt together with conductors which serve to couple the antenna arrangement to a connector via which signals are fed from the mobile to the antenna arrangement for transmission.